1. Field of the Invention
The present invention relates to a thin film magnetic head and a method of manufacturing the same, and more particularly to technique of improving a performance of an inductive type thin film writing magnetic head of a composite type thin film magnetic head constructed by stacking the inductive type thin film writing magnetic head and a magnetoresistive type reading magnetic head one on the other.
2. Description of the Related Art
Recently a surface recording density of a hard disc device has been improved, and it has been required to develop a thin film magnetic head having an improved performance accordingly. In order to improve a performance of a reading magnetic head, a reproducing head utilizing a magnetoresistive effect has been widely used. As the reproducing magnetic head utilizing the magnetoresistive effect, an AMR reproducing element utilizing a conventional anisotropic magnetoresistive (AMR) effect has been widely used. There has been further developed a GMR reproducing element utilizing a giant magnetoresistive (GMR) effect having a resistance change ratio higher than the normal anisotropic magnetoresistive effect by several times. In the present specification, these AMR and GMR reproducing elements are termed as a magnetoresistive reproducing element or MR reproducing element.
By using the AMR reproducing element, a very high surface recording density of several gigabits per a unit square inch has been realized, and a surface recording density can be further increased by using the GMR element. By increasing a surface recording density in this manner, it is possible to realize a hard disc device which has a very large storage capacity of more than 10 gigabytes and is still small in size.
A height of a magnetoresistive reproducing element is one of factors which determine a performance of a reproducing head including a magnetoresistive reproducing element. This height is generally called MR Height, here denoted by MRH. The MR height MRH is a distance measured from an air bearing surface on which one edge of the magnetoresistive reproducing element is exposed to the other edge of the element remote from the air bearing surface. During a manufacturing process of the magnetic head, a desired MR height MRH can be obtained by controlling an amount of polishing the air bearing surface.
At the same time, a performance of a recording head has been also required to be improved. In order to increase a surface recording density, it is necessary to make a track density on a magnetic record medium as high as possible. For this purpose, a width of a pole portion at the air bearing surface has to be reduced to a value within a range from several micron meters to several sub-micron meters. In order to satisfy such a requirement, the semiconductor manufacturing process has been adopted for manufacturing the thin film magnetic head. One of factors determining a performance of an inductive type thin film writing magnetic film is a throat height TH. This throat height TH is a distance of a pole portion measured from the air bearing surface to an edge of an insulating layer which serves to separate electrically a thin film coil from the air bearing surface. It has been required to shorten this distance as small as possible. Also this throat height TH is determined by an amount of polishing the air bearing surface.
FIGS. 1a, 1b-9a, 9b are cross sectional views showing successive steps of a known method of manufacturing a conventional typical thin film magnetic head, said cross sectional views being cut along a plane perpendicular to the air bearing surface and cut along a plane parallel with the air bearing surface. FIGS. 10-12 are a cross sectional view illustrating a completed thin film magnetic head cut along a plane perpendicular to the air bearing surface, a cross sectional view of the pole portion cut along a plane parallel with the air bearing surface, and a plan view depicting the pole portion. This magnetic head belongs to a composite type thin film magnetic head which is constructed by stacking an inductive type thin film writing magnetic head and a magnetoresistive type thin film reading magnetic head one on the other.
At first, as illustrated in FIGS. 1a and 1b, on a substrate 1 made of a hard non-magnetic material such as aluminum-titan-carbon (AlTiC), is deposited an insulating layer 2 made of alumina (Al.sub.2 O.sub.3) and having a thickness of about 5-10 .mu.m. Then, as depicted in FIGS. 2a and 2b, a bottom shield layer 3 constituting a magnetic shield for the MR reproducing magnetic head is formed to have a thickness of about 3 .mu.m on the insulating layer.
Then, after depositing by sputtering a shield gap layer 4 made of an alumina with a thickness of 100-150 nm as shown in FIGS. 3a and 3b, a magnetoresistive layer 5 having a thickness of several tens nano meters and being made of a material having the magnetoresistive effect, and the magnetoresistive layer is shaped into a desired pattern by a highly precise mask alignment.
Next, as represented in FIGS. 4a and 4b, a shield gap layer 6 is formed such that the electromagnetic layer 5 is embedded within the shield gap layers 4, 6.
Then a magnetic layer 7 made of a permalloy and having a thickness of 3 .mu.m is formed as shown in FIGS. 5a and 5b. This magnetic layer 7 serves not only as an upper shield layer for magnetically shielding the MR reproducing element together with the above mentioned bottom shield layer 3, but also as a bottom magnetic layer of the inductive type writing thin film magnetic head to be manufactured later. Here, for the sake of explanation, the magnetic layer 7 is called a first magnetic layer, because this magnetic layer constitutes one of magnetic layers forming the thin film writing magnetic head.
Next, after forming, on the first magnetic layer 7, a write gap layer 8 made of a nonmagnetic material such as alumina to have a thickness of about 200 nm, a second magnetic layer 8 made of a magnetic material having a high saturated magnetic flux density such as a permalloy (Ni: 50 wt %, Fe: 50 wt %) and iron nitride (FeN) and the second magnetic layer is shaped into a desired pattern by means of a precise mask alignment.
This second magnetic layer 24 having a desired pattern is called a pole chip and a track width is determined by a width of the pole chip.
During this process, a dummy pattern 9' for connecting the bottom pole (first magnetic layer) to an upper pole (third magnetic layer) to be formed later is formed. Then a through hole can be easily formed after mechanical polishing or chemical-mechanical polishing (CMP).
In order to prevent an increase of an effective track width, that is, in order to prevent a spread of a magnetic flux at the lower pole during a writing operation, the gap layer 8 and bottom pole (first magnetic layer) near the pole chip 9 are removed by an ion beam etching such as an ion milling. This condition is illustrated in FIG. 5, and this structure is called a trim structure. It should be noted that this portion constitutes the pole portion of the first magnetic layer.
Next, as illustrated in FIGS. 6a and 6b, an insulating layer 10 such as an alumina layer is formed to have a thickness of about 3 .mu.m, and then an assembly is flattened by, for instance CMP.
After that, an electrically insulating photo-resist layer 11 is formed in accordance with a given pattern by a highly precise mask alignment, and then a first layer of a thin film coil 12 made of, for instance copper is formed on the photo-resist layer 11.
Next, as depicted in FIGS. 7a and 7b, an insulating photo-resist layer 13 is formed on the thin film coil 12 by a highly precise mask alignment, a surface is flattened by baking at a temperature of, for instance 250-300.degree. C.
Furthermore, as shown in FIGS. 8a and 8b, on the thus flattened surface of the photo-resist layer 13, a second layer thin film coil 14 is formed. Then, a photo-resist layer 15 is formed on the second layer thin film coil 14 by a highly precise mask alignment, and a baking process is carried again at a temperature of, for instance 250.degree. C.
A reason for forming the photo-resist layers 11, 13 and 15 by a highly precise mask alignment is that the throat height TH and MR height are determined with respect to edges of these photo-resist layers on a side of the pole portion.
Next, as shown in FIGS. 9a and 9b, a third magnetic layer 16 made of, for instance a permalloy is formed on the second magnetic layer (pole chip) 9 and photo-resist layers 11, 13 and 15 such that the third magnetic layer has a thickness of 3 .mu.m and is shaped into a desired pattern.
The third magnetic layer 16 is brought into contact with the first magnetic layer 7 at a position remote from the pole portion by means of the dummy pattern 9', and therefore the thin film coil 12, 14 pass through a closed magnetic yoke structure constituted by the first, second and third magnetic layers.
Furthermore, an overcoat layer 25 made of an alumina is deposited on an exposed surface of the third magnetic layer 16.
Finally, a side wall at which the magnetoresistive layer 5 and gap layer 8 are formed is polished to form an air bearing surface (ABS) 18. During the formation of the air bearing surface 18, the magnetoresistive layer 5 is also polished to obtain an MR reproducing element 19. In this manner, the above mentioned throat height TH and MR height MRH are determined by the polishing. This condition is shown in FIG. 10. In an actual manufacturing process, contact pads for establishing electrical connections to the thin film coils 12, 14 and MR reproducing element 19 are formed, but these contact pads are not shown in the drawings.
As shown in FIG. 10, an angle .theta. between a straight line S connecting side edges of the photo-resist layers 11, 13 and 15 isolating the thin film coils 12, 14 and an upper surface of the third magnetic layer 16 is called an apex angle. This apex angle is one of important factors for determining a property of the thin film magnetic head together with the throat height TH and MR height MRH.
Furthermore, as shown in the plan view of FIG. 12, a width W of the pole portion 20 of the second magnetic layer 9 and third magnetic layer 16 is small. A width of tracks recorded on a record medium is determined by said width W, and therefore it is necessary to make this width W as small as possible in order to realize a high surface recording density. It should be noted that in the drawing, the thin film coils 12, 14 are denoted to be concentric for the sake of simplicity.
In the known method of manufacturing the thin film magnetic head, there is a special problem in the formation of the upper pole (yoke pole) after the formation of the thin film coil in a precise manner along the outwardly protruded coil portion, particularly along an inclined portion (apex) thereof, said coil portion being covered with the photo-resist insulating layers. That is to say, in the known method, upon forming the upper pole, after an upper pole material such as permalloy is deposited by plating on the outwardly protruded coil portion having a height of about 7-10 .mu.m, a photo-resist is applied to have a thickness of 3-4 .mu.m, and then the layer is shaped into a given pattern by utilizing the photolithography. Since a thickness of the photo-resist layer provided on the upper portion of the coil portion should be at least 3 .mu.m, the photo-resist layer has to be applied such that a portion of the photoresist at a bottom of the outwardly protruded coil portion would have a thickness of 8-10 .mu.m.
On the other hand, in order to form a narrow track of the recording head near the edges of the photo-resist insulating layers (for instance, layers 11 and 13 in FIG. 7), the upper pole formed on the write gap layer provided on the surface of the outwardly protruded coil portion as well as on the flat surface should be patterned to have a width of about 1 .mu.m, said coil portion and flat portion having a level difference of about 10 .mu.m. Therefore, it is necessary to form the photo-resist layer having a thickness of 8-10 .mu.m and a pattern having a width of 1 .mu.m.
However, when a narrow pattern having a width of 1 .mu.m is to be formed with the thick photo-resist layer having a thickness of 8-10 .mu.m, a top pole which can realize a narrow track could hardly be manufactured accurately due to a deformation of a pattern by light reflection during a light exposure in a photolithography and an inevitable decrease in a resolution caused by a large thickness of the photo-resist layer.
Under the above circumstances, as shown in the above explained known method, the above problem has been solved by writing data with the aid of the pole chip which can realize a narrow track width and after forming the pole chip, the upper pole is connected to the pole chip. That is to say, the division structure is adopted, in which the upper yoke is divided into the pole chip defining the track width and the upper pole for introducing a magnetic flux into the pole chip.
However, the thin film magnetic head, particularly the recording magnetic head formed in the above mentioned manner still has the following problems.
(1) The throat height TH and MR height MRH are determined, while the edge of the insulating layer isolating the thin film coil on a side of the pole portion is used as a positional reference, and the insulating layer is generally made of an organic insulating photo-resist layer and thus is liable to be affected by heat. Therefore, the insulating film is liable to be melt or softened by the heating treatment at about 250.degree. C. during the formation of the thin film coil, and a pattern of the insulating layer might be deformed. Moreover, a reference position of zero throat height is determined by an end of the pole chip 9 opposite to the air bearing surface 18, and the edge of the pole chip pattern is rounded off due to a fact that the pole chip has a narrow width W, and therefore a position of the end of the pole chip might be shifted. In this manner, in the composite type thin film magnetic head, it is difficult to determine the reference position of throat height zero accurately, and thus the thin film magnetic head having desired throat height TH and MR height MRH according to the desired design values could not be manufacture with a high yield. PA0 (2) The surface of the pole chip 9 is coupled with the surface of the third magnetic layer 16. In order to make the width W of the pole chip narrow as explained above and in order to attain a good magnetic property, a length of the pole chip has to be short such as about 1 .mu.m. Therefore, a contact area of the pole chip and third magnetic layer is small. Moreover, the third magnetic layer is brought into contact with the pole chip perpendicularly, and thus a magnetic flux is liable to be saturated at this portion, a writing property, particularly a magnetic flux rise time is degraded. PA0 (3) If there is an alignment error in the photolithography for forming the third magnetic layer 16 on the pole chip 9 having the narrow width W, a center of the pole chip 9 and a center of the pole portion 20 of the third magnetic layer 16 viewed from the air bearing surface might be shifted relative to each other. If the center of the pole chip 9 is deviated from the center of the pole portion 20 of the third magnetic layer 16, there might be produced a large leakage of the magnetic flux from the pole portion of the third magnetic layer and data might be written by this leaked magnetic flux. Therefore, an effective track width is increased and data might be recorded in a region other than a desired region into which the data has to be recorded.